1. Reid of the Invention
This invention relates to a method and apparatus for measuring eyeglass frames and lenses, and more particularly, to a method and apparatus for digitizing the coordinates of the outer edge of an eyeglass lens or the inner edge of an eyeglass frame by digitizing an image of a shadow of the lens or frame.
2. Description of Related Art
In the past, it was common for lenses used in eyeglasses to be ground by an optician. Grinding eyeglass lenses by hand is precise work that requires considerable skill and time. Grinding eyeglass lenses was commonly done by a limited number of specialists to whom a prescription would be sent. Additionally, the person grinding the lenses would need to be sent the associated eyeglass frame so that the lenses could be shaped to fit the frame.
More recently, it has become popular to stock standard lenses (referred to as "finished lenses") which are ground, cast, or otherwise made to conform to different prescriptions in quantity by a manufacturer. Such finished lenses may be polished, if necessary, and then distributed to optical outlets in order to reduce the time required to fill an eyeglass prescription, and to allow such prescriptions to be filled by people with less skill than is required to grind a lens to a prescribed curvature. By stocking finished lenses which are preground to most prescriptions at optical outlets which are conveniently located, the time required to fill an optical prescription is greatly reduced. Furthermore, since finished lenses can be manufactured in very large quantities, the cost of manufacture is also greatly reduced.
However, due to the large diversity in types and shapes of eyeglass frames, once a pair of finished lenses have been chosen, each finished lens must still be custom cut to fit within an eyeglass frame. No standards have been established in the eyeglass industry to control the shapes and sizes of lenses. Therefore, finished lenses are commonly fit to a frame by a process known as "edging". Initially, edging was performed by hand by skilled artisans. More recently, it has been common for a device known as an "edger" to be used. For example, one prior art method uses a tool which makes contact with, and mechanically traces the shape of, an eyeglass frame into which finished lenses are to be placed. The eyeglass frame is thus used to generate a template which can then be used to guide an edger. As the shape of the template is mechanically traced, a cutting arm is guided to cut the finished lens to fit within the eyeglass frame.
Alternatively, a prior art digitizer may be used to identify the shape and size of a lens and communicate digital data representative of the size and shape to which a lens must be edged to fit within a particular eyeglass frame. Such prior art digitizers make contact with the eyeglass frame and follow the contour of the frame to determine the size and shape of a lens that will fit within the frame.
The process is somewhat different when edging lenses for "frameless glasses", which do not have a complete enclosed frame which can be used to generate a template. In this case, an appropriate "dummy" lens is selected from a set of standard lens shapes and sizes and is used as the template. The edger mechanically traces the outside of the dummy lens, thus using the dummy lens as the template.
While the process of edging a finished lens using an edger is much more accurate and less difficult than manually edging a finished lens, the accuracy of the prior art edgers is such that finished lenses are not always edged properly. This is due in large part to the fact that each of the prior art methods rely upon mechanical contact with an eyeglass frame to determine the size and shape to which a finished lens is to be edged.
The present invention is a non-contact method and apparatus for determining the shape to which a finished lens should be cut in order to fit the finished lens within an eyeglass frame without the use of a template and with a relatively low level of user training and skill.